| Chromium is widely used in electroplating,dyes,medicine,leather and other industries.Chromium-containing pollutants are discharged into the environment,destroying the ecology and endangering human health.This paper takes Cr(Ⅵ)in the environment as the target pollutant,and uses waste agricultural biomass straw as raw material to prepare phosphoric acid modified biochar.Based on the characterization of the surface characteristics of the biochar,it is used to repair Cr(Ⅵ)in water and soil environment.The study reveals the main influencing factors and mechanism of the adsorption,removal and fixation of Cr(Ⅵ)by modified biochar.The preparation conditions of phosphoric acid modified biochar have been optimized:carbonization temperature was 500℃;the ratio of phosphoric acid modifier dosage to biomass mass ratio was 1:2.After biochar modification,the specific surface area and porosity were greatly increased,and the structure was more dispersed;the H/C ratio decreased,the O/C ratio increased,and the number of oxygen-containing functional groups on the surface increased;–COOH,C=O,C–O,COO-and other functional groups were strengthened after modification.The surface structure and properties of the modified biochar have been improved,and it has a higher adsorption potential.The adsorption and removal efficiency of modified biochar for Cr(Ⅵ)in solution was studied.The influence of main process factors(p H,initial concentration,dosage,temperature)on the removal of Cr(Ⅵ)was investigated.When p H=3 and solid-liquid ratio of 1:2000,the adsorption capacity of modified biochar on Cr(Ⅵ)can reach 112 mg/g,which is 5.1 times that of unmodified biochar.The adsorption of Cr(Ⅵ)by modified biochar conforms to the pseudo-second-order kinetic model.The adsorption process is mainly based on ion exchange and integration reactions.The Freundlich adsorption isotherm model is more suitable for describing the adsorption process of Cr(Ⅵ).It reveals the reduction mechanism and kinetics of Cr(Ⅵ)on the surface of biochar,as well as the influence of p H,adsorption capacity and temperature.The reduction of Cr(Ⅵ)affects the surface functional groups and charge of biochar,which is beneficial for the adsorption of total Cr.The effect of modified biochar on Cr(Ⅵ)contaminated soil was better than that of unmodified biochar.When the mass ratio of modified biochar to soil was 1:100,the amount of Cr(Ⅵ)extracted by Ca Cl2 in the contaminated soil with 500 mg/kg Cr(Ⅵ)was lower than the detection limit.The combination of Cr(III)formed by Cr(Ⅵ)reduction and soil components was conducive to the development of biochar ability.The remediation effect of Cr(Ⅵ)contaminated soil was closely related to the depth of soil layer,and the remediation load of the bottom soil was greater due to the migration of Cr(Ⅵ)from the upper layer.In summary,after the wheat straw biochar is modified by phosphoric acid,its specific surface area and surface functional groups increase,and the adsorption and reduction capacity of Cr(Ⅵ)is significantly improved.This study explored a new way to use agricultural biomass to prepare high-performance biochar,deepened the understanding of the occurrence and role of reduction in the process of biochar adsorption of Cr(Ⅵ),and revealed that biochar adsorbs and adsorbs in water and soil environments.The main influencing factors of fixed Cr(Ⅵ)provide theoretical basis and technical support for the practical application of biochar to remediate environmental chromium pollution. |
PDF Full Text Request